Tailored graphene nanoparticles for biomedical application: preliminary in vitro characterization of the functionality in model cell lines

Thanks to an environmentally friendly physical treatment of high purity graphite, a good control of the structure of graphene nanoparticles (GNPs) has been obtained with the production of stable and reproducible GNPs water dispersions. The preparation protocol entailed ball-milling of synthetic graphite followed by sonication in water and centrifugation/separation procedures. This way, two different GNPs samples with slightly different structural characteristics were harvested: TOP60, showing an average lateral size of the graphene layers <L> = 70 nm and average number of stacked layers <N> = 4, and BOTTOM60, with <L> = 120 nm and <N> = 6. A detailed structural characterization of GNPs was performed as mandatory pre-requisite to build reliable structure/properties correlations, in terms of both biomedical efficacy and toxicity, aiming at a rationale design of tailored materials for applications in biological environments. To this end, in this study GNPs were thoroughly characterized, focusing on cytotoxicity, cellular uptake, and inflammatory response, by testing their effect in different cell lines. BOTTOM60 GNPs in culture medium and in the presence of cells showed a tendency to form big aggregates, phenomenon that was probably responsible for their cytotoxicity at high concentrations. On the other hand, TOP60 GNPs showed a diverse behavior depending on the cell type under investigation. Indeed, the nanoparticles were internalized by cells specialized in endo/phagocytosis, such as astrocytoma cells, but not by carcinoma cells of epithelial origin. Moreover, TOP60 GNPs caused a reduction of proliferation only at high concentration and did not trigger an inflammatory response in THP-1-derived macrophages. The evidence here collected paves the way for further investigations towards the development of GNPs-based drug delivery systems.